Video encoding method and apparatus and video decoding method and apparatus

ABSTRACT

An image encoding method includes generating symbols by performing transformation and quantization according to a transformation block, on a block that performs prediction according to a prediction mode; updating a probability index of a current sub block by using a probability index of a previous sub block among sub blocks included in the transformation block; determining a rate according to a bit length of the current sub block by using the probably index; determining a rate of the transformation block by using rates of the sub blocks; determining a distortion by using a difference between an original image and a reconstruction image according to transformation and quantization; and determining a rate-distortion (R-D) cost by using the distortion and the rate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2015-0122090, filed on Aug. 28, 2015, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND

1. Field

The present disclosure relates to video encoding methods and apparatusesand video decoding methods and apparatuses in consideration of arate-distortion (R-D) cost.

2. Description of the Related Art

As hardware for reproducing and storing high resolution or high qualityvideo content is being developed and supplied, a need for a video codeccapable of effectively encoding or decoding the high resolution or highquality video content is increasing. According to a video codec of therelated art, a video is encoded according to a limited encoding methodbased on a macroblock having a predetermined size.

SUMMARY

Provided are video encoding methods and apparatuses and video decodingmethods and apparatuses in consideration of a rate-distortion (R-D)cost.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to an aspect of an embodiment, an image encoding methodincludes generating symbols by performing transformation andquantization according to a transformation block, on a block thatperforms prediction according to a prediction mode; updating aprobability index of a current sub block by using a probability index ofa previous sub block among sub blocks included in the transformationblock; determining a rate according to a bit length of the current subblock by using the probably index; determining a rate of thetransformation block by using rates of the sub blocks; determining adistortion by using a difference between an original image and areconstruction image according to transformation and quantization; anddetermining a rate-distortion (R-D) cost by using the distortion and therate.

At least one of the updating of the probability index of the current subblock, the determining of the rate, the determining of the rate of thetransformation block, the determining of the distortion, and thedetermining of the R-D cost may be performed in parallel according toone sub block.

The probability index of the current sub block may be an indexindicating a probability that a bin value encoded by using a contextused to encode the current sub block is a least probable symbol (LPS).

The updating of the probability index of the current sub block mayinclude: obtaining the probability index of the current sub block byreflecting values and a number of generated bins in a probability indexof a context of the previous sub block.

The determining of the distortion may include: normalizing thedistortion.

The normalizing the distortion may be performed by using a quantizationstep size with respect to the R-D cost.

The image encoding method may further include: determining a predictionmode having a minimum R-D cost among R-D costs determined for each ofone or more prediction modes.

According to an aspect of another embodiment, an image encodingapparatus includes a symbol generator configured to generate symbols byperforming transformation and quantization according to a transformationblock, on a block that performs prediction according to a predictionmode; a rate determiner configured to update a probability index of acurrent sub block by using a probability index of a previous sub blockamong sub blocks included in the transformation block, determine a rateaccording to a bit length of the current sub block by using the probablyindex, and determine a rate of the transformation block by using ratesof the sub blocks; a distortion determiner configured to determine adistortion by using a difference between an original image and areconstruction image according to transformation and quantization; and arate-distortion (R-D) cost determiner configured to determine a R-D costby using the distortion and the rate.

Operations by at least one of the rate determiner, the distortiondeterminer, and the R-D cost determiner may be performed in parallelaccording to one sub block

The probability index of the current sub block may be an indexindicating a probability that a bin value encoded by using a contextused to encode the current sub block is a least probable symbol (LPS).

The rate determiner may obtain the probability index of the current subblock by reflecting values and a number of generated bins in aprobability index of a context of the previous sub block.

The distortion determiner may perform normalizing the distortion.

The normalizing may be performed by using a quantization step size withrespect to the R-D cost.

The image encoding apparatus may further include: a prediction modedeterminer for determining a prediction mode having a minimum R-D costamong R-D costs determined for each of one or more prediction modes.

According to another aspect of an embodiment of the present invention,there is provided a non-transitory computer-readable recording mediumhaving recorded thereon a computer program for executing the method.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of a context-adaptive binary arithmetic coding(CABAC) encoding apparatus, according to a related art;

FIG. 2 is a block diagram of a video encoding apparatus, according to anembodiment;

FIG. 3 is a reference diagram for describing a rate determiner,according to an embodiment;

FIG. 4 is a reference diagram for describing a distortion determiner,according to an embodiment;

FIG. 5 is a reference flowchart of a method of determining arate-distortion (R-D) cost in a video encoding apparatus, according toan embodiment;

FIG. 6 is a block diagram of a video encoding apparatus, according toanother embodiment;

FIG. 7 is a block diagram of a video encoding apparatus based on codingunits according to a tree structure, according to various embodiments;

FIG. 8 is a block diagram of a video decoding apparatus based on codingunits according to a tree structure, according to various embodiments;

FIG. 9 is a diagram for describing a concept of coding units accordingto various embodiments;

FIG. 10 is a block diagram of an image encoder based on coding units,according to various embodiments;

FIG. 11 is a block diagram of an image decoder based on coding units,according to various embodiments;

FIG. 12 is a diagram illustrating deeper coding units and partitions,according to various embodiments;

FIG. 13 is a diagram for describing a relationship between a coding unitand transformation units, according to various embodiments;

FIG. 14 is a diagram for describing encoding information of codingunits, according to various embodiments;

FIG. 15 is a diagram of deeper coding units, according to an embodiment;

FIGS. 16 through 18 are diagrams for describing a relationship betweencoding units, prediction units, and transformation units, according tovarious embodiments;

FIG. 19 is a diagram for describing a relationship between a codingunit, a prediction unit, and a transformation unit, according toencoding mode information of Table 1;

FIG. 20 is a diagram of a physical structure of a disc in which aprogram is stored, according to various embodiments;

FIG. 21 is a diagram of a disc drive for recording and reading a programby using a disc;

FIG. 22 is a diagram of an overall structure of a content supply systemfor providing a content distribution service;

FIGS. 23 and 24 are diagrams respectively of an external structure andan internal structure of a mobile phone to which a video encoding methodand a video decoding method are applied, according to variousembodiments;

FIG. 25 is a diagram of a digital broadcast system to which acommunication system is applied, according to various embodiments; and

FIG. 26 is a diagram illustrating a network structure of a cloudcomputing system using a video encoding apparatus and a video decodingapparatus, according to various embodiments.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects thereof. Expressions such as “at least one of,” whenpreceding a list of elements, modify the entire list of elements and donot modify the individual elements of the list.

As used herein, terms such as “unit” and “module” indicate a unit forprocessing at least one function or operation, wherein the unit and theblock may be embodied as hardware or software or may be embodied bycombining hardware and software.

As used herein, the term “an embodiment” or “embodiments” of the presentinvention refers to properties, structures, features, and the like, thatare described in relation to at least one embodiment of the presentinventive concept. Thus, expressions such as “according to anembodiment” do not always refer to the same embodiment.

A video encoding method and a video decoding method in consideration ofa rate-distortion (R-D) cost will be described with reference to FIGS. 1through 6.

In addition, a video encoding method and a video decoding method, basedon coding units having a tree structure according to various embodimentswill be described with reference to FIGS. 7 through 26. Hereinafter, an‘image’ may denote a still image or a moving image of a video, or avideo itself.

FIG. 1 is a block diagram of a context-adaptive binary arithmetic coding(CABAC) encoding apparatus, according to the related art.

In a CABAC encoding process, discrete cosine transformation (DCT) may beperformed by a residual block unit, and then a syntax element may begenerated for each residual block unit.

Referring to FIG. 1, the CABAC encoding apparatus may include abinarizer 10, a context modeler 20, and a binary arithmetic coder 30.The binary arithmetic coder 30 may include a regular coding engine 32and a bypass coding engine 34.

If a non-binary valued syntax element is input, the binarizer 10 may mapa syntax element to a sequence having a binary value to output a binstring.

Among the bin string mapped to the binary value by the binarizer 10 anda syntax element having its own binary value, certain selected binvalues may be encoded by the bypass coding engine 34 and output asbitstreams, without undergoing processing by the context modeler 20, inorder to increase a processing speed of an encoding process, and otherbin values may be input to the context modeler 20. In this regard, thebin values indicate bits of the bin string.

The context modeler 20 may determine a probability model necessary forencoding input bin values or a currently input bin value based on apreviously encoded syntax element.

The regular coding engine 32 may perform arithmetic encoding on theinput bin values to generate bitstreams based on the probability modeldetermined by the context modeler 20.

FIG. 2 is a block diagram of a video encoding apparatus 100, accordingto an embodiment.

The video encoding apparatus 100 may encode video data of a spatialdomain through intra prediction/inter prediction, transformation,quantization, and symbol encoding.

The video encoding apparatus 100 according to an embodiment may includea symbol generator 11, a rate determiner 12, a distortion determiner 14,and a rate-distortion (R-D) cost determiner 16.

The video encoding apparatus 100 according to an embodiment may splitimage data of a video into a plurality of data units and encode theimage data for each data unit. A data unit may have a square shape, arectangular shape, or any geometric shape and is not limited to a dataunit having a certain size. In a video encoding method based on codingunits according to a tree structure, the data unit may be a largestcoding unit, a coding unit, a prediction unit, a transformation unit, orthe like. Examples of applying arithmetic encoding and decoding methodsaccording to an embodiment in video encoding and decoding methods basedon coding units having the tree structure will be described withreference to FIGS. 7 through 19 later.

For convenience of description, a video encoding method with respect toa ‘block’ that is a kind of data unit will be described below. However,video encoding methods according to various embodiments are not limitedto the video encoding method with respect to the ‘block’ and may beapplied to various data units.

The symbol generator 11 may perform transformation and quantization on ablock on which prediction is performed according to a prediction mode bya transformation block unit to generate symbols.

The rate determiner 12 may update a probability index of a current subblock by using a probability index of a previous sub block among subblocks included in a transformation block, may determine a rateaccording to a bit length of the current sub block by using theprobability index, and may determine a rate of the transformation blockby using the rate of sub blocks.

The distortion determiner 14 may include distortion betweenreconstruction images according to transformation and quantizationperformed on an original image.

The R-D cost determiner 16 may determine a R-D cost by using distortionand the rate of the transformation block.

The R-D cost according to an embodiment may be used to model arelationship between an amount of errors that occur according to a valueof a quantization parameter and a bit rate when performing a compressionprocess in a corresponding mode.

The R-D cost according to an embodiment may be calculated according toEquation 1 below.

J=D+lamda·R  [Equation 1]

J may denote the R-D cost. D may denote the distortion between thereconstruction images according to transformation and quantizationperformed on the original image. R may denote a length of a bitstream.lamda may denote a Lagrangian multiplier that is a coefficient dependingon the quantization parameter.

FIG. 3 is a reference diagram for describing the rate determiner 12,according to an embodiment.

The rate determiner 12 according to an embodiment may include aprediction mode operation rate determiner 22 and a transformation andquantization operation rate determiner 24.

The prediction mode operation rate determiner 22 according to anembodiment may determine a rate with respect to syntax elements of anintra mode and an inter mode by using a number of bin values, withoutusing a context value. Processes of the prediction mode operation ratedeterminer 22 according to an embodiment may be performed in parallelaccording to one sub block at one time in a hardware module

Table 1 below shows an example of a syntax element that may be used bythe prediction mode operation rate determiner 22 according to anembodiment.

TABLE 1 category syntax element list intra modeprev_intra_luma_pred_flag mpm_idx rem_intra_luma_pred_modeintra_chroma_pred_mode Merge merge_flag merge_idx AMVP inter_pred_idcref_idx_l0, ref_idx_l1 mvp_l0_flag, mvp_l1_flag MVD

Referring to Table 1 above, the prediction mode operation ratedeterminer 22 may use prev_intra_luma_pred_flag, mpm_idx,rem_intra_luma_pred_mode, and intra_chroma_pred_mode as syntax elementsfor encoding an intra mode.

prev_intra_luma_pred_flag is a syntax element indicating whether anintra prediction mode of a current prediction unit (PU) is a mostprobable mode (MPM). mpm_idx is a syntax element regarding three MPMs.rem_intra_luma_pred_mode is a syntax element indicating information ofother selected modes except for modes included in the MPM with respectto luma. intra_chroma_pred_mode is a syntax element indicatinginformation of an intra prediction mode of chroma.

Referring to Table 1 above, the prediction mode operation ratedeterminer 22 may use merge_flag and merge_idx as syntax elements forencoding a Merge mode.

merge_flag is a syntax element indicating whether the current PU ismerged with peripheral blocks. merge_idx is a syntax element indicatingwhich element of a merge list is merged.

Referring to Table 1 above, the prediction mode operation ratedeterminer 22 may use inter_pred_idc, ref_idx_I0, ref_idx_I1,mvp_I0_flag, mvp_I1_flag, and MVD (motion vector difference) as syntaxelements for encoding an AMVP (advanced motion vector predition) mode.

inter_pred_idc is a syntax element for a prediction direction of a PU.ref_idx_I0 and ref_idx_I1 are syntax elements for a reference frameindex. mvp_I0_flag and mvp_I1_flag are syntax elements for motion vectorprediction.

The transformation and quantization operation rate determiner 24according to an embodiment may determine rates with respect to a modeand a residual.

The transformation and quantization operation rate determiner 24according to an embodiment may determine rates by using the number ofbins with respect to syntax elements such as a coding unit (CU) mode, aPU mode, a coded block flag (CBF) mode, etc. without using a contextvalue. The transformation and quantization operation rate determiner 24may determine a rate with respect to a syntax element of the residual byusing a bitstream generated by performing regular encoding or bypasscoding.

For example, in regular coding, bin values input based on a probabilitymodel determined by a context modeler may be arithmetic encoded andoutput as bitstreams. In bypass coding, among a bin string mapped to abinary value and a syntax element having its own binary value, certainselected bin values may be bypass encoded and output as bitstreams.

Table 2 below shows an example of a syntax element that may be used bythe transformation and quantization operation rate determiner 24according to an embodiment.

TABLE 2 category syntax element list Mode CU, split_cu_flag PU modecu_skip_flag pred_mode_flag part_mode intra modeprev_intra_luma_pred_flag mpm_idx rem_intra_luma_pred_modeintra_chroma_pred_mode Merge merge_flag merge_idx AMVP inter_pred_idcref_idx_l0, ref_idx_l1 mvp_l0_flag, mvp_l1_flag MVD CBF rqt_root_cbfcbf_luma cbf_cb/cbf_cr Residual transform_skip_flaglast_sig_coeff_x_prefix, last_sig_coeff_y_prefix,last_sig_coeff_x_suffix, last_sig_coeff_y_suffix, coded_sub_block_flag,sig_coeff_flag, coeff_abs_level_greater1_flag,coeff_abs_level_greater2_flag, coeff_sign_flag,coeff_abs_level_remaining

Referring to Table 2 above, the transformation and quantizationoperation rate determiner 24 may use split_cu_flag, cu_skip_flag,pred_mode_flag, and part_mode as syntax elements for encoding a CU and aPU mode.

split_cu_flag is a syntax element indicating whether to split a currentcoding quadtree. cu_skip_flag is a syntax element indicating whether toskip a current CU. pred_mode_flag is a syntax element indicating aprediction mode of the CU.

Referring to Table 2 above, the transformation and quantizationoperation rate determiner 24 may use rqt_root_cbf, cbf_luma, andcbf_cb/cbf_cr as syntax elements for encoding a CBF.

rqt_root_cbf is a syntax element indicating whether to call a syntax.cbf_luma and cbf_cb/cbf_cr are syntax elements signaling CBFs withrespect to brightness, Cb, and Cr TB, respectively.

Referring to Table 2 above, the transformation and quantizationoperation rate determiner 24 may use transform_skip_flag,last_sig_coeff_x_prefix, last_sig_coeff_y_prefix,last_sig_coeff_x_suffix, last_sig_coeff_y_suffix, coded_sub_block_flag,sig_coeff_flag, coeff_abs_level_greater1_flag,coeff_abs_level_greater2_flag, coeff_abs_level_remaining, andcoeff_sign_flag as syntax elements for encoding a residual.

transform_skip_flag is a syntax element indicating whether to skiptransformation. last_sig_coeff_x_prefix, last_sig_coeff_y_prefix,last_sig_coeff_x_suffix, and last_sig_coeff_y_suffix are syntax elementsindicating position information of a quantization level other than 0 ona final position when transformation units (TUs) are scanned in aspecific scanning order. coded_sub_block_flag is a syntax elementindicating whether a coefficient other than 0 is present in a TU by a4×4 block unit sig_coeff_flag is a syntax element having a value of 1when a quantization coefficient has a value greater than 0.coeff_abs_level_greater1_flag is a syntax element having a value of 1when an absolute value of a quantization level has a value greaterthan 1. coeff_abs_level_greater2_flag is a syntax element having a valueof 1 when the absolute value of the quantization level has a valuegreater than 2. coeff_abs_level_remaining is a syntax element indicatinga difference value between the absolute value of the quantization leveland a baselevel. coeff_sign_flag is a syntax element having a value of 1when the quantization level is a negative number and a value of 0 whenthe quantization level is a positive number.

Processes of the transformation and quantization operation ratedeterminer 24 according to an embodiment may be performed in parallelaccording to one sub block at one time in a hardware module so as tocalculate a rate with respect to a residual. In transformation andquantization, since only a rate of an entire TU is calculated, the rateof the entire TU may be calculated by collecting rates that occur whensub blocks are processed.

More specifically, the transformation and quantization operation ratedeterminer 24 may determine the rate with respect to the residual bymultiplying the number of bin values for each context with respect to aregular bin value by a rate estimation table value in regular coding,and may determine the rate as the number of bin values with respect to abypass bin value in bypass coding. The rate estimation table may includean index including a probability that an encoded bin value is a leastprobable symbol (LPS). The rate estimation table according to anembodiment may map values of vaIMPS and pStateIdx to a linearprobability value in which a bin value is 1 by using 7 bits (128) inorder to process a plurality of bin values in one context at a time.vaIMPS is an index indicating a value of a most probable symbol (MPS).pStateIdx is an index indicating a probability of the LPS.

The transformation and quantization operation rate determiner 24according to an embodiment may update context without considering a binvalue occurrence order so as to calculate the rate with respect to theresidual. A probability index of a current sub block may be obtained byreflecting values and number of occurred bin values to a probabilityindex with respect to context of a previous sub block. Morespecifically, when a window size is 16, a probability index update maybe calculated according to Equation 2 below.

$\begin{matrix}\begin{matrix}{\begin{matrix}{{{prob}\; 1{Idx}_{new}} = {{{\frac{16 - N}{16} \cdot {prob}}\; 1{Idx}_{old}} + {\frac{N}{16} \cdot}}} \\{{prob}\; 1{Idx}_{current}}\end{matrix},} & {{{if}\mspace{14mu} N} < 16} \\{{{{prob}\; 1{Idx}_{new}} = {{P_{current}\left( {{bin} = 1} \right)} \times 128}},} & {else}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

N=n₀+n₁ and n₀ denotes the number of bin values having a value of 1.prob1Idx_(new) denotes a probability index of context of an updatedcurrent sub block. prob1Idx_(old) denotes a probability index of contextof a previous sub block. prob1Idx_(current) denotes a probability indexof context of a current sub block.

FIG. 4 is a reference diagram for describing the distortion determiner14, according to an embodiment.

The distortion determiner 14 according to an embodiment may include alamda normalizer 33 and a distortion normalizer 35.

The lamda normalizer 33 according to an embodiment may be expressedaccording to Equation 3 below.

$\begin{matrix}{{{lamda}_{n} = {\frac{lamda}{{N(s)} \cdot Q_{step}^{2}} = {{alpha} \cdot W_{k} \cdot 2^{- \frac{8}{3}}}}},{{N(s)} = 2^{{2\; s} - 14}},{{{where}\mspace{11mu} s} = {{\log_{2}\left( {{TB}\mspace{11mu} {size}} \right)}.}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Q_(step) denotes a quantization step size and may be expressed by aquantization parameter (QP). N(s), alpha, and W_(k) denote coefficientsindicating lamda_(n). TB size means a size of a TU.

The distortion normalizer 35 according to an embodiment may be expressedaccording to Equation4 below.

$\begin{matrix}{D_{n} = {\frac{D}{{N(s)} \cdot Q_{step}^{2}} = {\sum\limits_{i}{\sum\limits_{k}{\left( {l_{{ik},{real}} - I_{ik}} \right)^{2}.}}}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

I_(ik,real) denotes a real number value expressing a value obtained byquantizing a transformation coefficient to decimal places. I_(ik)denotes an integer value by removing values of decimal places from thevalue obtained by quantizing the transformation coefficient. Accordingto Equation 3 above, a range of lamda of Equation 1 may be reducedthrough normalization. According to Equation 4 above, a process ofcalculating N(s)·Q_(step) may be removed from D of Equation 1 throughnormalization.

Processes of the lamda normalizer 33 and the distortion normalizer 35according to an embodiment may be performed in parallel according to onesub block at one time in a hardware module

FIG. 5 is a reference flowchart of a method of determining a R-D cost ina video encoding apparatus, according to an embodiment.

In operation S3010, the symbol generator 11 may perform predictionaccording to a prediction mode and perform transformation andquantization according to a transformation block.

For example, the intra mode and the inter mode may be performed onpartitions of 2N×2N, 2N×N, N×2N, and N×N. The skip mode may be performedonly on the partition of 2N×2N. Encoding is independently performed onone prediction unit in a coding unit, and thus, a prediction mode havinga least encoding error is selected.

An image encoding apparatus may perform transformation on image data ina coding unit based not only on the coding unit for encoding the imagedata, but also based on a data unit that is different from the codingunit. In order to perform transformation in the coding unit,transformation may be performed based on a transformation unit having asize smaller than or equal to the coding unit. For example, atransformation block unit may include a data unit for an intra mode anda transformation unit for an inter mode. a transformation andquantization operation rate determiner 24

In operation S3020, the rate determiner 12 may update a probabilityindex of a current sub block. Operation S3020 corresponds to update aprobalbility index of a current sub block described with respect to thetransformation and quantization operation rate determiner 24 of FIG. 3and is described in detail in relation to Equation 2, and thus adescription thereof is omitted here.

In operation S3030, the rate determiner 12 may determine a rateaccording to a bit length of the current sub block. In operation S3040,the rate determiner 12 may determine a rate of a transformation block.The rate determiner 12 may determine the rate by using the predictionmode operation rate determiner 22 and the transformation andquantization operation rate determiner 24 of FIG. 3.

In operation S3050, the R-D cost determiner 16 may determine the R-Dcost. The R-D cost according to an embodiment may determine the R-D costby using the rate R determined by the rate determiner 12, the distortionD determined by the distortion determiner 14, and lamda. “Processes ofthe R-D cost determiner 16 according to an embodiment may be performedin parallel according to one sub block at one time in a hardware module

FIG. 6 is a block diagram of a video encoding apparatus, according toanother embodiment.

The prediction mode determiner 18 may determine a prediction mode havinga minimum R-D cost among R-D costs determined with respect to at leastone prediction mode, for each prediction mode. “Processes of theprediction mode determiner 18 according to an embodiment may beperformed in parallel according to one sub block at one time in ahardware module

In video encoding apparatus 100 according to an embodiment, as describedabove, video data may be split into larges coding units (LCUs), each LCUmay be encoded and decoded based on coding units having a treestructure. Hereinafter, a video encoding method and a video decodingmethod based on the coding units having the tree structure according tovarious embodiments will be described with reference to FIGS. 7 through26.

FIG. 7 is a block diagram of the video encoding apparatus 100 based oncoding units according to a tree structure, according to an embodiment.

The video encoding apparatus 100 involving video prediction based oncoding units according to a tree structure includes a LCU splitter 110,a coding unit determiner 120, and an outputter 130.

The coding unit determiner 120 of FIG. 7 according to an embodiment mayinclude the symbol generator 11, the rate determiner 12, the distortiondeterminer 14, and the R-D cost determiner 16.

The LCU splitter 110 may split a current picture based on a LCU that isa coding unit having a maximum size for a current picture of an image.If the current picture is larger than the LCU, image data of the currentpicture may be split into the at least one LCU. The LCU according to anembodiment may be a data unit having a size of 32×32, 64×64, 128×128,256×256, etc., wherein a shape of the data unit is a square having awidth and length in squares of 2. The image data may be output to thecoding unit determiner 120 according to the at least one LCU.

A coding unit according to an embodiment may be characterized by amaximum size and a depth. The depth denotes the number of times thecoding unit is spatially split from the LCU, and as the depth deepens,deeper coding units according to depths may be split from the LCU to asmallest coding unit (SCU). A depth of the LCU is an uppermost depth anda depth of the SCU is a lowermost depth. Since a size of a coding unitcorresponding to each depth decreases as the depth of the LCU deepens, acoding unit corresponding to an upper depth may include a plurality ofcoding units corresponding to lower depths.

As described above, the image data of the current picture is split intothe LCUs according to a maximum size of the coding unit, and each of theLCUs may include deeper coding units that are split according to depths.Since the LCU according to an embodiment is split according to depths,the image data of the space domain included in the LCU may behierarchically classified according to depths.

A maximum depth and a maximum size of a coding unit, which limit thetotal number of times a height and a width of the LCU are hierarchicallysplit, may be predetermined.

The coding unit determiner 120 encodes at least one split regionobtained by splitting a region of the LCU according to depths, anddetermines a depth to output a finally encoded image data according tothe at least one split region. In other words, the coding unitdeterminer 120 determines a depth by encoding the image data in thedeeper coding units according to depths, according to the LCU of thecurrent picture, and selecting a depth having the least encoding error.The determined depth and the encoded image data according to thedetermined depth are output to the outputter 130.

The image data in the LCU is encoded based on the deeper coding unitscorresponding to at least one depth equal to or below the maximum depth,and results of encoding the image data are compared based on each of thedeeper coding units. A depth having the least encoding error may beselected after comparing encoding errors of the deeper coding units. Atleast one depth may be selected for each LCU.

The size of the LCU is split as a coding unit is hierarchically splitaccording to depths, and as the number of coding units increases. Also,even if coding units correspond to the same depth in one LCU, it isdetermined whether to split each of the coding units corresponding tothe same depth to a lower depth by measuring an encoding error of theimage data of the each coding unit, separately. Accordingly, even whenimage data is included in one LCU, the encoding errors may differaccording to regions in the one LCU, and thus the depths may differaccording to regions in the image data. Thus, one or more depths may bedetermined in one LCU, and the image data of the LCU may be dividedaccording to coding units of at least one depth.

Accordingly, the coding unit determiner 120 may determine coding unitshaving a tree structure included in the LCU. The ‘coding units having atree structure’ according to an embodiment include coding unitscorresponding to a depth determined to be the depth, from among alldeeper coding units included in the LCU. A coding unit of a depth may behierarchically determined according to depths in the same region of theLCU, and may be independently determined in different regions.Similarly, a depth in a current region may be independently determinedfrom a depth in another region.

A maximum depth according to an embodiment is an index related to thenumber of splitting times from a LCU to an SCU. A first maximum depthaccording to an embodiment may denote the total number of splittingtimes from the LCU to the SCU. A second maximum depth according to anembodiment may denote the total number of depth levels from the LCU tothe SCU. For example, when a depth of the LCU is 0, a depth of a codingunit, in which the LCU is split once, may be set to 1, and a depth of acoding unit, in which the LCU is split twice, may be set to 2. Here, ifthe SCU is a coding unit in which the LCU is split four times, 5 depthlevels of depths 0, 1, 2, 3, and 4 exist, and thus the first maximumdepth may be set to 4, and the second maximum depth may be set to 5.

Prediction encoding and transformation may be performed according to theLCU. The prediction encoding and the transformation are also performedbased on the deeper coding units according to a depth equal to or depthsless than the maximum depth, according to the LCU.

Since the number of deeper coding units increases whenever the LCU issplit according to depths, encoding, including the prediction encodingand the transformation, is performed on all of the deeper coding unitsgenerated as the depth deepens. For convenience of description, theprediction encoding and the transformation will now be described basedon a coding unit of a current depth, in a LCU.

The video encoding apparatus 100 may variously select a size or shape ofa data unit for encoding the image data. In order to encode the imagedata, operations, such as prediction encoding, transformation, andentropy encoding, are performed, and at this time, the same data unitmay be used for all operations or different data units may be used foreach operation.

For example, the video encoding apparatus 100 may select not only acoding unit for encoding the image data, but also a data unit differentfrom the coding unit so as to perform the prediction encoding on theimage data in the coding unit.

In order to perform prediction encoding in the LCU, the predictionencoding may be performed based on a coding unit corresponding to adepth, i.e., based on a coding unit that is no longer split to codingunits corresponding to a lower depth. Hereinafter, the coding unit thatis no longer split and becomes a basis unit for prediction encoding willnow be referred to as a ‘prediction unit’. A partition obtained bysplitting the prediction unit may include a prediction unit or a dataunit obtained by splitting at least one of a height and a width of theprediction unit. A partition is a data unit where a prediction unit of acoding unit is split, and a prediction unit may be a partition havingthe same size as a coding unit.

For example, when a coding unit of 2N×2N (where N is a positive integer)is no longer split and becomes a prediction unit of 2N×2N, and a size ofa partition may be 2N×2N, 2N×N, N×2N, or N×N. Examples of a partitionmode include symmetrical partitions that are obtained by symmetricallysplitting a height or width of the prediction unit, partitions obtainedby asymmetrically splitting the height or width of the prediction unit,such as 1:n or n:1, partitions that are obtained by geometricallysplitting the prediction unit, and partitions having arbitrary shapes.

A prediction mode of the prediction unit may be at least one of an intramode, a inter mode, and a skip mode. For example, the intra mode or theinter mode may be performed on the partition of 2N×2N, 2N×N, N×2N, orN×N. Also, the skip mode may be performed only on the partition of2N×2N. The encoding is independently performed on one prediction unit ina coding unit, thereby selecting a prediction mode having a leastencoding error.

The video encoding apparatus 100 may also perform the transformation onthe image data in a coding unit based not only on the coding unit forencoding the image data, but also based on a data unit that is differentfrom the coding unit. In order to perform the transformation in thecoding unit, the transformation may be performed based on a data unithaving a size smaller than or equal to the coding unit. For example, thedata unit for the transformation may include a data unit for an intramode and a data unit for an inter mode.

The transformation unit in the coding unit may be recursively split intosmaller sized regions in the similar manner as the coding unit accordingto the tree structure. Thus, residues in the coding unit may be dividedaccording to the transformation unit having the tree structure accordingto transformation depths.

A transformation depth indicating the number of splitting times to reachthe transformation unit by splitting the height and width of the codingunit may also be set in the transformation unit. For example, in acurrent coding unit of 2N×2N, a transformation depth may be 0 when thesize of a transformation unit is 2N×2N, may be 1 when the size of thetransformation unit is N×N, and may be 2 when the size of thetransformation unit is N/2×N/2. In other words, the transformation unithaving the tree structure may be set according to the transformationdepths.

Encoding information according to coding units corresponding to a depthrequires not only information about the depth, but also aboutinformation related to prediction encoding and transformation.Accordingly, the coding unit determiner 120 not only determines a depthhaving a least encoding error, but also determines a partition mode in aprediction unit, a prediction mode according to prediction units, and asize of a transformation unit for transformation.

Coding units according to a tree structure in a LCU and methods ofdetermining a prediction unit/partition, and a transformation unit,according to an embodiment, will be described in detail below withreference to FIGS. 9 through 19.

The coding unit determiner 120 may measure an encoding error of deepercoding units according to depths by using Rate-Distortion Optimizationbased on Lagrangian multipliers.

The outputter 130 outputs the image data of the LCU, which is encodedbased on the at least one depth determined by the coding unit determiner120, and information about the encoding mode according to the depth, inbitstreams.

The encoded image data may be obtained by encoding residues of an image.

The information about the encoding mode according to depth may includeinformation about the depth, about the partition mode in the predictionunit, the prediction mode, and the size of the transformation unit.

The information about the depth may be defined by using splittinginformation according to depths, which indicates whether encoding isperformed on coding units of a lower depth instead of a current depth.If the current depth of the current coding unit is the depth, image datain the current coding unit is encoded and output, and thus the splittinginformation may be defined not to split the current coding unit to alower depth. Alternatively, if the current depth of the current codingunit is not the depth, the encoding is performed on the coding unit ofthe lower depth, and thus the splitting information may be defined tosplit the current coding unit to obtain the coding units of the lowerdepth.

If the current depth is not the depth, encoding is performed on thecoding unit that is split into the coding unit of the lower depth. Sinceat least one coding unit of the lower depth exists in one coding unit ofthe current depth, the encoding is repeatedly performed on each codingunit of the lower depth, and thus the encoding may be recursivelyperformed for the coding units having the same depth.

Since the coding units having a tree structure are determined for oneLCU, and information about at least one encoding mode is determined fora coding unit of a depth, information about at least one encoding modemay be determined for one LCU. Also, a depth of the image data of theLCU may be different according to locations since the image data ishierarchically split according to depths, and thus splitting informationmay be set for the image data.

Accordingly, the outputter 130 may assign corresponding splittinginformation to at least one of the coding unit, the prediction unit, anda minimum unit included in the LCU.

The minimum unit according to an embodiment is a square data unitobtained by splitting the SCU constituting the lowermost depth by 4.Alternatively, the minimum unit according to an embodiment may be amaximum square data unit that may be included in all of the codingunits, prediction units, partition units, and transformation unitsincluded in the LCU.

For example, the encoding information output by the outputter 130 may beclassified into encoding information according to deeper coding units,and encoding information according to prediction units. The encodinginformation according to the deeper coding units may include theinformation about the prediction mode and about the size of thepartitions. The encoding information according to the prediction unitsmay include information about an estimated direction of an inter mode,about a reference image index of the inter mode, about a motion vector,about a chroma component of an intra mode, and about an interpolationmethod of the intra mode.

Information about a maximum size of the coding unit defined according topictures, slices, or GOPs, and information about a maximum depth may beinserted into a header of a bitstream, a sequence parameter set, or apicture parameter set.

Information about a maximum size of the transformation unit permittedwith respect to a current video, and information about a minimum size ofthe transformation unit may also be output through a header of abitstream, a sequence parameter set, or a picture parameter set. Theoutputter 130 may encode and output SAO parameters related to the SAOoperation described above with reference to FIGS. 1A through 14.

In the video encoding apparatus 100, the deeper coding unit may be acoding unit obtained by dividing a height or width of a coding unit ofan upper depth, which is one layer above, by two. In other words, whenthe size of the coding unit of the current depth is 2N×2N, the size ofthe coding unit of the lower depth is N×N. Also, the coding unit withthe current depth having a size of 2N×2N may include a maximum of 4 ofthe coding units with the lower depth.

Accordingly, the video encoding apparatus 100 may form the coding unitshaving the tree structure by determining coding units having an optimumshape and an optimum size for each LCU, based on the size of the LCU andthe maximum depth determined considering characteristics of the currentpicture. Also, since encoding may be performed on each LCU by using anyone of various prediction modes and transformations, an optimum encodingmode may be determined considering characteristics of the coding unit ofvarious image sizes.

Thus, if an image having a high resolution or a large data amount isencoded in a conventional macroblock, the number of macroblocks perpicture excessively increases. Accordingly, the number of pieces ofcompressed information generated for each macroblock increases, and thusit is difficult to transmit the compressed information and datacompression efficiency decreases. However, by using the video encodingapparatus 100, image compression efficiency may be increased since acoding unit is adjusted while considering characteristics of an imagewhile increasing a maximum size of a coding unit while considering asize of the image.

The video encoding apparatus 100 of FIG. 7 may perform operation of thevideo encoding apparatus 10 described above with reference to FIGS. 1and 6.

FIG. 8 is a block diagram of the video decoding apparatus 200 based oncoding units having a tree structure, according to an embodiment.

The video decoding apparatus 200 that involves video prediction based oncoding units having a tree structure includes a receiver 210, an imagedata and encoding information extractor 220, and an image data decoder230.

Definitions of various terms, such as a coding unit, a depth, aprediction unit, a transformation unit, and information about variousencoding modes, for decoding operations of the video decoding apparatus200 are identical to those described with reference to FIG. 7 and thevideo encoding apparatus 100.

The receiver 210 receives and parses a bitstream of an encoded video.The image data and encoding information extractor 220 extracts encodedimage data for each coding unit from the parsed bitstream, wherein thecoding units have a tree structure according to each LCU, and outputsthe extracted image data to the image data decoder 230. The image dataand encoding information extractor 220 may extract information about amaximum size of a coding unit of a current picture, from a header aboutthe current picture, a sequence parameter set, or a picture parameterset.

Also, the image data and encoding information extractor 220 extractssplitting information and encoding information for the coding unitshaving a tree structure according to each LCU, from the parsedbitstream. The extracted splitting information and encoding informationare output to the image data decoder 230. In other words, the image datain a bit stream is split into the LCU so that the image data decoder 230decodes the image data for each LCU.

The splitting information and encoding information according to the LCUmay be set for at least one piece of splitting information correspondingto the depth, and encoding information according to the depth mayinclude information about a partition mode of a corresponding codingunit corresponding to the depth, information about a prediction mode,and splitting information of a transformation unit. Also, splittinginformation according to depths may be extracted as the informationabout a final depth.

The splitting information and the encoding information according to eachLCU extracted by the image data and encoding information extractor 220is splitting information and encoding information determined to generatea minimum encoding error when an encoder, such as the video encodingapparatus 100, repeatedly performs encoding for each deeper coding unitaccording to depths according to each LCU. Accordingly, the videodecoding apparatus 200 may reconstruct an image by decoding the imagedata according to a depth and an encoding mode that generates theminimum encoding error.

Since the splitting information and the encoding information may beassigned to a predetermined data unit from among a corresponding codingunit, a prediction unit, and a minimum unit, the image data and encodinginformation extractor 220 may extract the splitting information and theencoding information according to the predetermined data units. Ifsplitting information and encoding information of a corresponding LCUare recorded according to predetermined data units, the predetermineddata units to which the same splitting information and encodinginformation are assigned may be inferred to be the data units includedin the same LCU.

The image data decoder 230 reconstructs the current picture by decodingthe image data in each LCU based on the splitting information and theencoding information according to the LCUs. In other words, the imagedata decoder 230 may decode the encoded image data based on theextracted information about the partition mode, the prediction mode, andthe transformation unit for each coding unit from among the coding unitshaving the tree structure included in each LCU. A decoding process mayinclude a prediction including intra prediction and motion compensation,and an inverse transformation.

The image data decoder 230 may perform intra prediction or motioncompensation according to a partition and a prediction mode of eachcoding unit, based on the information about the partition mode and theprediction mode of the prediction unit of the coding unit according todepths.

In addition, the image data decoder 230 may read information about atransformation unit according to a tree structure for each coding unitso as to perform inverse transformation based on transformation unitsfor each coding unit, for inverse transformation for each LCU. Via theinverse transformation, a pixel value of the space domain of the codingunit may be reconstructed.

The image data decoder 230 may determine a final depth of a current LCUby using splitting information according to depths. If the splittinginformation indicates that image data is no longer split in the currentdepth, the current depth is the final depth. Accordingly, the image datadecoder 230 may decode encoded data in the current LCU by using theinformation about the partition mode of the prediction unit, theinformation about the prediction mode, and the splitting information ofthe transformation unit for each coding unit corresponding to the depth.

In other words, data units containing the encoding information includingthe same splitting information may be gathered by observing the encodinginformation set assigned for the predetermined data unit from among thecoding unit, the prediction unit, and the minimum unit, and the gathereddata units may be considered to be one data unit to be decoded by theimage data decoder 230 in the same encoding mode. As such, the currentcoding unit may be decoded by obtaining the information about theencoding mode for each coding unit.

FIG. 9 is a diagram for describing a concept of coding units accordingto various embodiments.

A size of a coding unit may be expressed by width×height, and may be64×64, 32×32, 16×16, and 8×8. A coding unit of 64×64 may be split intopartitions of 64×64, 64×32, 32×64, or 32×32, and a coding unit of 32×32may be split into partitions of 32×32, 32×16, 16×32, or 16×16, a codingunit of 16×16 may be split into partitions of 16×16, 16×8, 8×16, or 8×8,and a coding unit of 8×8 may be split into partitions of 8×8, 8×4, 4×8,or 4×4.

In video data 310, a resolution is 1920×1080, a maximum size of a codingunit is 64, and a maximum depth is 2. In video data 320, a resolution is1920×1080, a maximum size of a coding unit is 64, and a maximum depth is3. In video data 330, a resolution is 352×288, a maximum size of acoding unit is 16, and a maximum depth is 1. The maximum depth shown inFIG. 9 denotes a total number of splits from a LCU to a minimum decodingunit.

If a resolution is high or a data amount is large, a maximum size of acoding unit may be large so as to not only increase encoding efficiencybut also to accurately reflect characteristics of an image. Accordingly,the maximum size of the coding unit of the video data 310 and 320 havinga higher resolution than the video data 330 may be 64.

Since the maximum depth of the video data 310 is 2, coding units 315 ofthe vide data 310 may include a LCU having a long axis size of 64, andcoding units having long axis sizes of 32 and 16 since depths aredeepened to two layers by splitting the LCU twice. Since the maximumdepth of the video data 330 is 1, coding units 335 of the video data 330may include a LCU having a long axis size of 16, and coding units havinga long axis size of 8 since depths are deepened to one layer bysplitting the LCU once.

Since the maximum depth of the video data 320 is 3, coding units 325 ofthe video data 320 may include a LCU having a long axis size of 64, andcoding units having long axis sizes of 32, 16, and 8 since the depthsare deepened to 3 layers by splitting the LCU three times. As a depthdeepens, detailed information may be precisely expressed.

FIG. 10 is a block diagram of an image encoder 400 based on codingunits, according to an embodiment.

The image encoder 400 performs operations necessary for encoding imagedata in the coding unit determiner 120 of the video encoding apparatus100. In other words, an intra predictor 420 performs intra prediction oncoding units in an intra mode according to prediction units, from amonga current frame 405, and an inter predictor 415 performs interprediction on coding units in an inter mode by using a current image 405and a reference image obtained from a reconstructed picture buffer 410according to prediction units. The current image 405 may be split intoLCUs and then the LCUs may be sequentially encoded. In this regard, theLCUs that are to be split into coding units having a tree structure maybe encoded.

The symbol generator 11 of FIG. 4 according to an embodiment may includeprevious processes of a bitstream 440 of FIG. 10, and the ratedeterminer 12, the distortion determiner 14, and the R-D cost determiner16 of FIG. 4 may include a process of using the bitstream 440 of FIG.10.

Residue data is generated by removing prediction data regarding codingunits of each mode that is output from the intra predictor 420 or theinter predictor 415 from data regarding encoded coding units of thecurrent image 405, and is output as a quantized transformationcoefficient according to transformation units through a transformer 425and a quantizer 430. The quantized transformation coefficient isreconstructed as the residue data in a space domain through adequantizer 445 and an inverse transformer 450. The reconstructedresidue data in the space domain is added to prediction data for codingunits of each mode that is output from the intra predictor 420 or theinter predictor and thus is reconstructed as data in a space domain forcoding units of the current image 405. The reconstructed data in thespace domain is generated as reconstructed images through a de-blocker455 and an SAO performer 460 and the reconstructed images are stored inthe reconstructed picture buffer 410. The reconstructed images stored inthe reconstructed picture buffer 410 may be used as reference images forinter prediction of another image. The transformation coefficientquantized by the transformer 425 and the quantizer 430 may be output asthe bitstream 440 through an entropy encoder 435.

In order for the image encoder 400 to be applied in the video encodingapparatus 100, all elements of the image encoder 400, i.e., the interpredictor 415, the intra predictor 420, the transformer 425, thequantizer 430, the entropy encoder 435, the dequantizer 445, the inversetransformer 450, the de-blocker 455, and the SAO performer 460, performoperations based on each coding unit among coding units having a treestructure according to each LCU.

In particular, the intra predictor 410, the motion estimator 420, andthe motion compensator 425 determines partitions and a prediction modeof each coding unit from among the coding units having a tree structurewhile considering the maximum size and the maximum depth of a currentLCU, and the transformer 430 determines the size of the transformationunit in each coding unit from among the coding units having a treestructure.

Specifically, the intra predictor 420 and the inter predictor 415 maydetermine a partition mode and a prediction mode of each coding unitamong the coding units having a tree structure in consideration of amaximum size and a maximum depth of a current LCU, and the transformer425 may determine whether to split a transformation unit having a quadtree structure in each coding unit among the coding units having a treestructure.

FIG. 11 is a block diagram of an image decoder 500 based on codingunits, according to an embodiment.

An entropy decoder 515 parses encoded image data to be decoded andinformation about encoding required for decoding from a bitstream 505.The encoded image data is a quantized transformation coefficient fromwhich residue data is reconstructed by a dequantizer 520 and an inversetransformer 525.

An intra predictor 540 performs intra prediction on coding units in anintra mode according to each prediction unit. An inter predictor 535performs inter prediction on coding units in an inter mode from amongthe current image 405 for each prediction unit by using a referenceimage obtained from a reconstructed picture buffer 530.

Prediction data and residue data regarding coding units of each mode,which passed through the intra predictor 540 and the inter predictor535, are summed, and thus data in a space domain regarding coding unitsof the current image 405 may be reconstructed, and the reconstructeddata in the space domain may be output as a reconstructed image 560through a de-blocker 545 and an SAO performer 550. Reconstructed imagesstored in the reconstructed picture buffer 530 may be output asreference images.

In order to decode the image data in the image data decoder 230 of thevideo decoding apparatus 200, operations after the entropy decoder 515of the image decoder 500 according to an embodiment may be performed.

In order for the image decoder 500 to be applied in the video decodingapparatus 200 according to an embodiment, all elements of the imagedecoder 500, i.e., the entropy decoder 515, the dequantizer 520, theinverse transformer 525, the inter predictor 535, the de-blocker 545,and the SAO performer 550 may perform operations based on coding unitshaving a tree structure for each LCU.

In particular, the SAO performer 550 and the inter predictor 535 maydetermine a partition and a prediction mode for each of the coding unitshaving a tree structure, and the inverse transformer 525 may determinewhether to split a transformation unit having a quad tree structure foreach of the coding units.

FIG. 12 is a diagram illustrating deeper coding units according todepths, and partitions, according to an embodiment.

The video encoding apparatus 100 and the video decoding apparatus 200use hierarchical coding units so as to consider characteristics of animage. A maximum height, a maximum width, and a maximum depth of codingunits may be adaptively determined according to the characteristics ofthe image, or may be differently set by a user. Sizes of deeper codingunits according to depths may be determined according to thepredetermined maximum size of the coding unit.

In a hierarchical structure 600 of coding units, according to anembodiment, the maximum height and the maximum width of the coding unitsare each 64, and the maximum depth is 3. In this case, the maximum depthrefers to a total number of times the coding unit is split from the LCUto the SCU. Since a depth deepens along a vertical axis of thehierarchical structure 600, a height and a width of the deeper codingunit are each split. Also, a prediction unit and partitions, which arebases for prediction encoding of each deeper coding unit, are shownalong a horizontal axis of the hierarchical structure 600.

In other words, a coding unit 610 is a LCU in the hierarchical structure600, wherein a depth is 0 and a size, i.e., a height by width, is 64×64.The depth deepens along the vertical axis, and a coding unit 620 havinga size of 32×32 and a depth of 1, a coding unit 630 having a size of16×16 and a depth of 2, and a coding unit 640 having a size of 8×8 and adepth of 3. The coding unit 640 having a size of 8×8 and a depth of 3 isan SCU.

The prediction unit and the partitions of a coding unit are arrangedalong the horizontal axis according to each depth. In other words, ifthe coding unit 610 having a size of 64×64 and a depth of 0 is aprediction unit, the prediction unit may be split into partitionsinclude in the encoding unit 610, i.e. a partition 610 having a size of64×64, partitions 612 having the size of 64×32, partitions 614 havingthe size of 32×64, or partitions 616 having the size of 32×32.

Similarly, a prediction unit of the coding unit 620 having the size of32×32 and the depth of 1 may be split into partitions included in thecoding unit 620, i.e. a partition 620 having a size of 32×32, partitions622 having a size of 32×16, partitions 624 having a size of 16×32, andpartitions 626 having a size of 16×16.

Similarly, a prediction unit of the coding unit 630 having the size of16×16 and the depth of 2 may be split into partitions included in thecoding unit 630, i.e. a partition having a size of 16×16 included in thecoding unit 630, partitions 632 having a size of 16×8, partitions 634having a size of 8×16, and partitions 636 having a size of 8×8.

Similarly, a prediction unit of the coding unit 640 having the size of8×8 and the depth of 3 may be split into partitions included in thecoding unit 640, i.e. a partition having a size of 8×8 included in thecoding unit 640, partitions 642 having a size of 8×4, partitions 644having a size of 4×8, and partitions 646 having a size of 4×4.

In order to determine a final depth of the coding units constituting theLCU 610, the coding unit determiner 120 of the video encoding apparatus100 performs encoding for coding units corresponding to each depthincluded in the LCU 610.

A number of deeper coding units according to depths including data inthe same range and the same size increases as the depth deepens. Forexample, four coding units corresponding to a depth of 2 are required tocover data that is included in one coding unit corresponding to a depthof 1. Accordingly, in order to compare encoding results of the same dataaccording to depths, the coding unit corresponding to the depth of 1 andfour coding units corresponding to the depth of 2 are each encoded.

In order to perform encoding for a current depth from among the depths,a least encoding error may be selected for the current depth byperforming encoding for each prediction unit in the coding unitscorresponding to the current depth, along the horizontal axis of thehierarchical structure 600. Alternatively, the minimum encoding errormay be searched for by comparing the least encoding errors according todepths, by performing encoding for each depth as the depth deepens alongthe vertical axis of the hierarchical structure 600. A depth and apartition having the minimum encoding error in the coding unit 610 maybe selected as the final depth and a partition mode of the coding unit610.

FIG. 13 is a diagram for describing a relationship between a coding unit710 and transformation units 720, according to an embodiment.

The video encoding apparatus 100 or the video decoding apparatus 200encodes or decodes an image according to coding units having sizessmaller than or equal to a LCU for each LCU. Sizes of transformationunits for transformation during encoding may be selected based on dataunits that are not larger than a corresponding coding unit.

For example, in the video encoding apparatus 100 or the video decodingapparatus 200, if a size of the coding unit 710 is 64×64, transformationmay be performed by using the transformation units 720 having a size of32×32.

Also, data of the coding unit 710 having the size of 64×64 may beencoded by performing the transformation on each of the transformationunits having the size of 32×32, 16×16, 8×8, and 4×4, which are smallerthan 64×64, and then a transformation unit having the least coding errormay be selected.

FIG. 14 is a diagram for describing encoding information of coding unitscorresponding to a depth, according to an embodiment.

The outputter 130 of the video encoding apparatus 100 may encode andtransmit information 800 about a partition mode, information 810 about aprediction mode, and information 820 about a size of a transformationunit for each coding unit corresponding to a final depth, as informationabout an encoding mode.

The information 800 indicates information about a mode of a partitionobtained by splitting a prediction unit of a current coding unit,wherein the partition is a data unit for prediction encoding the currentcoding unit. For example, a current coding unit CU_0 having a size of2N×2N may be split into any one of a partition 802 having a size of2N×2N, a partition 804 having a size of 2N×N, a partition 806 having asize of N×2N, and a partition 808 having a size of N×N. Here, theinformation 800 about the partition mode is set to indicate one of thepartition 804 having a size of 2N×N, the partition 806 having a size ofN×2N, and the partition 808 having a size of N×N.

The information 810 indicates a prediction mode of each partition. Forexample, the information 810 may indicate a mode of prediction encodingperformed on a partition indicated by the information 800, i.e., anintra mode 812, an inter mode 814, or a skip mode 816.

The information 820 indicates a transformation unit to be based on whentransformation is performed on a current coding unit. For example, thetransformation unit may be a first intra transformation unit 822, asecond intra transformation unit 824, a first inter transformation unit826, or a second inter transformation unit 828.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information 800, 810, and820 for decoding, according to each deeper coding unit.

FIG. 15 is a diagram of deeper coding units according to depths,according to an embodiment.

Splitting information may be used to indicate a change of a depth. Thespilt information indicates whether a coding unit of a current depth issplit into coding units of a lower depth.

A prediction unit 910 for prediction encoding a coding unit 900 having adepth of 0 and a size of 2N_0×2N_0 may include partitions of a partitionmode 912 having a size of 2N_0×2N_0, a partition mode 914 having a sizeof 2N_0×N_0, a partition mode 916 having a size of N_0×2N_0, and apartition mode 918 having a size of N_0×N_0. FIG. 23 only illustratesthe partition modes 912 through 918 which are obtained by symmetricallysplitting the prediction unit 910, but a partition mode is not limitedthereto, and the partitions of the prediction unit 910 may includeasymmetrical partitions, partitions having a predetermined shape, andpartitions having a geometrical shape.

Prediction encoding is repeatedly performed on one partition having asize of 2N_0×2N_0, two partitions having a size of 2N_0×N_0, twopartitions having a size of N_0×2N_0, and four partitions having a sizeof N_0×N_0, according to each partition mode. The prediction encoding inan intra mode and an inter mode may be performed on the partitionshaving the sizes of 2N_0×2N_0, N_0×2N_0, 2N_0×N_0, and N_0×N_0. Theprediction encoding in a skip mode is performed only on the partitionhaving the size of 2N_0×2N_0.

If an encoding error is smallest in one of the partition modes 912through 916, the prediction unit 910 may not be split into a lowerdepth.

If the encoding error is the smallest in the partition mode 918, a depthis changed from 0 to 1 to split the partition mode 918 in operation 920,and encoding is repeatedly performed on coding units 930 having a depthof 2 and a size of N_0×N_0 to search for a minimum encoding error.

A prediction unit 940 for prediction encoding the coding unit 930 havinga depth of 1 and a size of 2N_1×2N_1 (=N_0×N_0) may include partitionsof a partition mode 942 having a size of 2N_1×2N_1, a partition mode 944having a size of 2N_1×N_1, a partition mode 946 having a size ofN_1×2N_1, and a partition mode 948 having a size of N_1×N_1.

If an encoding error is the smallest in the partition mode 948, a depthis changed from 1 to 2 to split the partition mode 948 in operation 950,and encoding is repeatedly performed on coding units 960, which have adepth of 2 and a size of N_2×N_2 to search for a minimum encoding error.

When a maximum depth is d, split operation according to each depth maybe performed up to when a depth becomes d−1, and splitting informationmay be encoded as up to when a depth is one of 0 to d−2. In other words,when encoding is performed up to when the depth is d−1 after a codingunit corresponding to a depth of d−2 is split in operation 970, aprediction unit 990 for prediction encoding a coding unit 980 having adepth of d−1 and a size of 2N_(d−1)×2N_(d−1) may include partitions of apartition mode 992 having a size of 2N_(d−1)×2N_(d−1), a partition mode994 having a size of 2N_(d−1)×N_(d−1), a partition mode 996 having asize of N_(d−1)×2N_(d−1), and a partition mode 998 having a size ofN_(d−1)×N_(d−1).

Prediction encoding may be repeatedly performed on one partition havinga size of 2N_(d−1)×2N_(d−1), two partitions having a size of2N_(d−1)×N_(d−1), two partitions having a size of N_(d−1)×2N_(d−1), fourpartitions having a size of N_(d−1)×N_(d−1) from among the partitionmodes 992 through 998 to search for a partition mode having a minimumencoding error.

Even when the partition mode 998 has the minimum encoding error, since amaximum depth is d, a coding unit CU_(d−1) having a depth of d−1 is nolonger split to a lower depth, and a depth for the coding unitsconstituting a current LCU 900 is determined to be d−1 and a partitionmode of the current LCU 900 may be determined to be N_(d−1)×N_(d−1).Also, since the maximum depth is d and an SCU 980 having a lowermostdepth of d−1 is no longer split to a lower depth, splitting informationfor the SCU 980 is not set.

A data unit 999 may be a ‘minimum unit’ for the current LCU. A minimumunit according to an embodiment may be a square data unit obtained bysplitting an SCU 980 by 4. By performing the encoding repeatedly, thevideo encoding apparatus 100 may select a depth having the leastencoding error by comparing encoding errors according to depths of thecoding unit 900 to determine a depth, and set a corresponding partitionmode and a prediction mode as an encoding mode of the depth.

As such, the minimum encoding errors according to depths are compared inall of the depths of 1 through d, and a depth having the least encodingerror may be determined as a depth. The depth, the partition mode of theprediction unit, and the prediction mode may be encoded and transmittedas information about an encoding mode. Also, since a coding unit issplit from a depth of 0 to a depth, only splitting information of thedepth is set to 0, and splitting information of depths excluding thedepth is set to 1.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information about thedepth and the prediction unit of the coding unit 900 to decode thepartition 912. The video decoding apparatus 200 may determine a depth,in which splitting information is 0, as a depth by using splittinginformation according to depths, and use information about an encodingmode of the corresponding depth for decoding.

FIGS. 16 through 18 are diagrams for describing a relationship betweencoding units 1010, prediction units 1060, and transformation units 1070,according to an embodiment.

The coding units 1010 are coding units having a tree structure,corresponding to depths determined by the video encoding apparatus 100,in a LCU. The prediction units 1060 are partitions of prediction unitsof each of the coding units 1010, and the transformation units 1070 aretransformation units of each of the coding units 1010.

When a depth of a LCU is 0 in the coding units 1010, depths of codingunits 1012 and 1054 are 1, depths of coding units 1014, 1016, 1018,1028, 1050, and 1052 are 2, depths of coding units 1020, 1022, 1024,1026, 1030, 1032, and 1048 are 3, and depths of coding units 1040, 1042,1044, and 1046 are 4.

In the prediction units 1060, some encoding units 1014, 1016, 1022,1032, 1048, 1050, 1052, and 1054 are obtained by splitting the codingunits in the encoding units 1010. In other words, partition modes in thecoding units 1014, 1022, 1050, and 1054 have a size of 2N×N, partitionmodes in the coding units 1016, 1048, and 1052 have a size of N×2N, anda partition mode of the coding unit 1032 has a size of N×N. Predictionunits and partitions of the coding units 1010 are smaller than or equalto each coding unit.

Transformation or inverse transformation is performed on image data ofthe coding unit 1052 in the transformation units 1070 in a data unitthat is smaller than the coding unit 1052. Also, the coding units 1014,1016, 1022, 1032, 1048, 1050, and 1052 in the transformation units 1070are different from those in the prediction units 1060 in terms of sizesand shapes. In other words, the video encoding and decoding apparatuses100 and 200 may perform intra prediction, motion estimation, motioncompensation, transformation, and inverse transformation individually ona data unit in the same coding unit.

Accordingly, encoding is recursively performed on each of coding unitshaving a hierarchical structure in each region of a LCU to determine anoptimum coding unit, and thus coding units having a recursive treestructure may be obtained. Encoding information may include splittinginformation about a coding unit, information about a partition mode,information about a prediction mode, and information about a size of atransformation unit. Table 3 shows the encoding information that may beset by the video encoding and decoding apparatuses 100 and 200.

TABLE 3 Splitting information 0 (Encoding on Coding Unit having Size of2N × 2N and Current Depth of d) Size of Transformation Unit SplittingSplitting Partition mode information 0 information 1 SymmetricalAsymmetrical of of Prediction Partition Partition TransformationTransformation Splitting Mode mode mode Unit Unit information 1 Intra 2N× 2N 2N × nU 2N × 2N N × N Repeatedly Inter 2N × N 2N × nD (SymmetricalEncode Skip N × 2N nL × 2N Type) Coding Units (Only N × N nR × 2N N/2 ×N/2 having 2N × 2N) (Asymmetrical Lower Depth Type) of d + 1

The outputter 130 of the video encoding apparatus 100 may output theencoding information about the coding units having a tree structure, andthe image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract the encoding information about thecoding units having a tree structure from a received bitstream.

Splitting information indicates whether a current coding unit is splitinto coding units of a lower depth. If splitting information of acurrent depth d is 0, a depth, in which a current coding unit is nolonger split into a lower depth, is a final depth, and thus informationabout a partition mode, prediction mode, and a size of a transformationunit may be defined for the final depth. If the current coding unit isfurther split according to the splitting information, encoding isindependently performed on four split coding units of a lower depth.

A prediction mode may be one of an intra mode, an inter mode, and a skipmode. The intra mode and the inter mode may be defined in all partitionmodes, and the skip mode is defined only in a partition mode having asize of 2N×2N.

The information about the partition mode may indicate symmetricalpartition modes having sizes of 2N×2N, 2N×N, N×2N, and N×N, which areobtained by symmetrically splitting a height or a width of a predictionunit, and asymmetrical partition modes having sizes of 2N×nU, 2N×nD,nL×2N, and nR×2N, which are obtained by asymmetrically splitting theheight or width of the prediction unit. The asymmetrical partition modeshaving the sizes of 2N×nU and 2N×nD may be respectively obtained bysplitting the height of the prediction unit in 1:3 and 3:1, and theasymmetrical partition modes having the sizes of nL×2N and nR×2N may berespectively obtained by splitting the width of the prediction unit in1:3 and 3:1

The size of the transformation unit may be set to be two types in theintra mode and two types in the inter mode. In other words, if splittinginformation of the transformation unit is 0, the size of thetransformation unit may be 2N×2N, which is the size of the currentcoding unit. If splitting information of the transformation unit is 1,the transformation units may be obtained by splitting the current codingunit. Also, if a partition mode of the current coding unit having thesize of 2N×2N is a symmetrical partition mode, a size of atransformation unit may be N×N, and if the partition mode of the currentcoding unit is an asymmetrical partition mode, the size of thetransformation unit may be N/2×N/2.

The encoding information about coding units having a tree structure mayinclude at least one of a coding unit corresponding to a depth, aprediction unit, and a minimum unit. The coding unit corresponding tothe depth may include at least one of a prediction unit and a minimumunit containing the same encoding information.

Accordingly, it is determined whether adjacent data units are includedin the same coding unit corresponding to the depth by comparing encodinginformation of the adjacent data units. Also, a corresponding codingunit corresponding to a depth is determined by using encodinginformation of a data unit, and thus a distribution of depths in a LCUmay be determined.

Accordingly, if a current coding unit is predicted based on encodinginformation of adjacent data units, encoding information of data unitsin deeper coding units adjacent to the current coding unit may bedirectly referred to and used.

Alternatively, if a current coding unit is predicted based on encodinginformation of adjacent data units, data units adjacent to the currentcoding unit are searched using encoded information of the data units,and the searched adjacent coding units may be referred for predictingthe current coding unit.

FIG. 19 is a diagram for describing a relationship between a codingunit, a prediction unit, and a transformation unit, according toencoding mode information of Table 3.

A LCU 1300 includes coding units 1302, 1304, 1306, 1312, 1314, 1316, and1318 of depths. Here, since the coding unit 1318 is a coding unit of adepth, splitting information may be set to 0. Information about apartition mode of the coding unit 1318 having a size of 2N×2N may be setto be one of a partition mode 1322 having a size of 2N×2N, a partitionmode 1324 having a size of 2N×N, a partition mode 1326 having a size ofN×2N, a partition mode 1328 having a size of N×N, a partition mode 1332having a size of 2N×nU, a partition mode 1334 having a size of 2N×nD, apartition mode 1336 having a size of nL×2N, and a partition mode 1338having a size of nR×2N.

Splitting information (TU size flag) of a transformation unit is a typeof a transformation index. The size of the transformation unitcorresponding to the transformation index may be changed according to aprediction unit type or partition mode of the coding unit.

For example, when the partition mode is set to be symmetrical, i.e. thepartition mode 1322, 1324, 1326, or 1328, a transformation unit 1342having a size of 2N×2N is set if a TU size flag of a transformation unitis 0, and a transformation unit 1344 having a size of N×N is set if a TUsize flag is 1.

When the partition mode is set to be asymmetrical, i.e., the partitionmode 1332, 1334, 1336, or 1338, a transformation unit 1352 having a sizeof 2N×2N is set if a TU size flag is 0, and a transformation unit 1354having a size of N/2×N/2 is set if a TU size flag is 1.

Referring to FIG. 19, the TU size flag is a flag having a value or 0 or1, but the TU size flag is not limited to 1 bit, and a transformationunit may be hierarchically split having a tree structure while the TUsize flag increases from 0. Splitting information (TU size flag) of atransformation unit may be an example of a transformation index.

In this case, the size of a transformation unit that has been actuallyused may be expressed by using a TU size flag of a transformation unit,according to an embodiment, together with a maximum size and minimumsize of the transformation unit. The video encoding apparatus 100 iscapable of encoding maximum transformation unit size information,minimum transformation unit size information, and a maximum TU sizeflag. The result of encoding the maximum transformation unit sizeinformation, the minimum transformation unit size information, and themaximum TU size flag may be inserted into an SPS. The video decodingapparatus 200 may decode video by using the maximum transformation unitsize information, the minimum transformation unit size information, andthe maximum TU size flag.

For example, (a) if the size of a current coding unit is 64×64 and amaximum transformation unit size is 32×32, (a−1) then the size of atransformation unit may be 32×32 when a TU size flag is 0, (a−2) may be16×16 when the TU size flag is 1, and (a−3) may be 8×8 when the TU sizeflag is 2.

As another example, (b) if the size of the current coding unit is 32×32and a minimum transformation unit size is 32×32, (b−1) then the size ofthe transformation unit may be 32×32 when the TU size flag is 0. Here,the TU size flag cannot be set to a value other than 0, since the sizeof the transformation unit cannot be less than 32×32.

As another example, (c) if the size of the current coding unit is 64×64and a maximum TU size flag is 1, then the TU size flag may be 0 or 1.Here, the TU size flag cannot be set to a value other than 0 or 1.

Thus, if it is defined that the maximum TU size flag is‘MaxTransformSizelndex’, a minimum transformation unit size is‘MinTransformSize’, and a transformation unit size is RootTuSize′ whenthe TU size flag is 0, then a current minimum transformation unit size‘CurrMinTuSize’ that can be determined in a current coding unit, may bedefined by Equation (1):

CurrMinTuSize=max(MinTransformSize,RootTuSize/(2̂MaxTransformSizelndex))  (1)

Compared to the current minimum transformation unit size ‘CurrMinTuSize’that can be determined in the current coding unit, a transformation unitsize ‘RootTuSize’ when the TU size flag is 0 may denote a maximumtransformation unit size that can be selected in the system. In Equation(1), RootTuSize/(2̂MaxTransformSizelndex)′ denotes a transformation unitsize when the transformation unit size ‘RootTuSize’, when the TU sizeflag is 0, is split a number of times corresponding to the maximum TUsize flag, and ‘MinTransformSize’ denotes a minimum transformation size.Thus, a smaller value from among ‘RootTuSize/(2̂MaxTransformSizeIndex)’and ‘MinTransformSize’ may be the current minimum transformation unitsize ‘CurrMinTuSize’ that can be determined in the current coding unit.

According to an embodiment, the maximum transformation unit sizeRootTuSize may vary according to the type of a prediction mode.

For example, if a current prediction mode is an inter mode, then‘RootTuSize’ may be determined by using Equation (2) below. In Equation(2), ‘MaxTransformSize’ denotes a maximum transformation unit size, andPUSize′ denotes a current prediction unit size.

RootTuSize=min(MaxTransformSize,PUSize)  (2)

That is, if the current prediction mode is the inter mode, thetransformation unit size ‘RootTuSize’, when the TU size flag is 0, maybe a smaller value from among the maximum transformation unit size andthe current prediction unit size.

If a prediction mode of a current partition unit is an intra mode,‘RootTuSize’ may be determined by using Equation (3) below. In Equation(3), ‘PartitionSize’ denotes the size of the current partition unit.

RootTuSize=min(MaxTransformSize,PartitionSize)  (3)

That is, if the current prediction mode is the intra mode, thetransformation unit size ‘RootTuSize’ when the TU size flag is 0 may bea smaller value from among the maximum transformation unit size and thesize of the current partition unit.

However, the current maximum transformation unit size ‘RootTuSize’ thatvaries according to the type of a prediction mode in a partition unit isjust an example and the embodiments are not limited thereto.

According to the video encoding method based on coding units having atree structure as described with reference to FIGS. 7 through 19, imagedata of the space domain is encoded for each coding unit of a treestructure. According to the video decoding method based on coding unitshaving a tree structure, decoding is performed for each LCU toreconstruct image data of the space domain. Thus, a picture and a videothat is a picture sequence may be reconstructed. The reconstructed videomay be reproduced by a reproducing apparatus, stored in a storagemedium, or transmitted through a network.

Offset parameters may be signaled with respect to each picture, eachslice, each LCU, each of coding units having a tree structure, eachprediction unit of the coding units, or each transformation unit of thecoding units. For example, pixel values of reconstructed pixels of eachLCU may be adjusted by using offset values reconstructed based onreceived offset parameters, and thus an LCU having a minimized errorbetween an original block and the LCU may be reconstructed.

For convenience of description, the video encoding method describedabove with reference to FIGS. 1 through 18, will be referred to as a‘video encoding method. In addition, the video decoding method describedabove with reference to FIGS. 1 through 18, will be referred to as a‘video decoding method’.

A computer-readable recording medium storing a program, e.g., a disc26000, according to various embodiments will now be described in detail.

FIG. 20 is a diagram of a physical structure of the disc 26000 in whicha program is stored, according to an embodiment. The disc 26000, whichis a storage medium, may be a hard drive, a compact disc-read onlymemory (CD-ROM) disc, a Blu-ray disc, or a digital versatile disc (DVD).The disc 26000 includes a plurality of concentric tracks Tr that areeach divided into a specific number of sectors Se in a circumferentialdirection of the disc 26000. In a specific region of the disc 26000, aprogram that executes the quantization parameter determination method,the video encoding method, and the video decoding method described abovemay be assigned and stored.

A computer system embodied using a storage medium that stores a programfor executing the video encoding method and the video decoding method asdescribed above will now be described with reference to FIG. 22.

FIG. 21 is a diagram of a disc drive 26800 for recording and reading aprogram by using the disc 26000. A computer system 26700 may store aprogram that executes at least one of a video encoding method and avideo decoding method according to an embodiment, in the disc 26000 viathe disc drive 26800. To run the program stored in the disc 26000 in thecomputer system 26700, the program may be read from the disc 26000 andbe transmitted to the computer system 26700 by using the disc drive26700.

The program that executes at least one of a video encoding method and avideo decoding method according to an embodiment may be stored not onlyin the disc 26000 illustrated in FIG. 20 or 21 but also in a memorycard, a ROM cassette, or a solid state drive (SSD).

A system to which the video encoding method and a video decoding methoddescribed above are applied will be described below.

FIG. 22 is a diagram of an overall structure of a content supply system11000 for providing a content distribution service. A service area of acommunication system is divided into predetermined-sized cells, andwireless base stations 11700, 11800, 11900, and 12000 are installed inthese cells, respectively.

The content supply system 11000 includes a plurality of independentdevices. For example, the plurality of independent devices, such as acomputer 12100, a personal digital assistant (PDA) 12200, a video camera12300, and a mobile phone 12500, are connected to the Internet 11100 viaan internet service provider 11200, a communication network 11400, andthe wireless base stations 11700, 11800, 11900, and 12000.

However, the content supply system 11000 is not limited to asillustrated in FIG. 22, and devices may be selectively connectedthereto. The plurality of independent devices may be directly connectedto the communication network 11400, not via the wireless base stations11700, 11800, 11900, and 12000.

The video camera 12300 is an imaging device, e.g., a digital videocamera, which is capable of capturing video images. The mobile phone12500 may employ at least one communication method from among variousprotocols, e.g., Personal Digital Communications (PDC), Code DivisionMultiple Access (CDMA), Wideband-Code Division Multiple Access (W-CDMA),Global System for Mobile Communications (GSM), and Personal HandyphoneSystem (PHS).

The video camera 12300 may be connected to a streaming server 11300 viathe wireless base station 11900 and the communication network 11400. Thestreaming server 11300 allows content received from a user via the videocamera 12300 to be streamed via a real-time broadcast. The contentreceived from the video camera 12300 may be encoded using the videocamera 12300 or the streaming server 11300. Video data captured by thevideo camera 12300 may be transmitted to the streaming server 11300 viathe computer 12100.

Video data captured by a camera 12600 may also be transmitted to thestreaming server 11300 via the computer 12100. The camera 12600 is animaging device capable of capturing both still images and video images,similar to a digital camera. The video data captured by the camera 12600may be encoded using the camera 12600 or the computer 12100. Softwarethat performs encoding and decoding video may be stored in acomputer-readable recording medium, e.g., a CD-ROM disc, a floppy disc,a hard disc drive, an SSD, or a memory card, which may be accessible bythe computer 12100.

If video data is captured by a camera built in the mobile phone 12500,the video data may be received from the mobile phone 12500.

The video data may also be encoded by a large scale integrated circuit(LSI) system installed in the video camera 12300, the mobile phone12500, or the camera 12600.

The content supply system 11000 may encode content data recorded by auser using the video camera 12300, the camera 12600, the mobile phone12500, or another imaging device, e.g., content recorded during aconcert, and transmit the encoded content data to the streaming server11300. The streaming server 11300 may transmit the encoded content datain a type of a streaming content to other clients that request thecontent data.

The clients are devices capable of decoding the encoded content data,e.g., the computer 12100, the PDA 12200, the video camera 12300, or themobile phone 12500. Thus, the content supply system 11000 allows theclients to receive and reproduce the encoded content data. Also, thecontent supply system 11000 allows the clients to receive the encodedcontent data and decode and reproduce the encoded content data in realtime, thereby enabling personal broadcasting.

Encoding and decoding operations of the plurality of independent devicesincluded in the content supply system 11000 may be similar to those of avideo encoding apparatus and a video decoding apparatus according to anembodiment.

The mobile phone 12500 included in the content supply system 11000according to an embodiment will now be described in greater detail withreferring to FIGS. 23 and 24.

FIG. 23 illustrates an external structure of the mobile phone 12500 towhich a video encoding method and a video decoding method are applied,according to an embodiment. The mobile phone 12500 may be a smart phone,the functions of which are not limited and a large number of thefunctions of which may be changed or expanded.

The mobile phone 12500 includes an internal antenna 12510 via which aradio-frequency (RF) signal may be exchanged with the wireless basestation 12000 of FIG. 21, and includes a display screen 12520 fordisplaying images captured by a camera 12530 or images that are receivedvia the antenna 12510 and decoded, e.g., a liquid crystal display (LCD)or an organic light-emitting diode (OLED) screen. The mobile phone 12500includes an operation panel 12540 including a control button and a touchpanel. If the display screen 12520 is a touch screen, the operationpanel 12540 further includes a touch sensing panel of the display screen12520. The mobile phone 12500 includes a speaker 12580 for outputtingvoice and sound or another type of sound outputter, and a microphone12550 for inputting voice and sound or another type sound inputter. Themobile phone 12500 further includes the camera 12530, such as acharge-coupled device (CCD) camera, to capture video and still images.The mobile phone 12500 may further include a storage medium 12570 forstoring encoded/decoded data, e.g., video or still images captured bythe camera 12530, received via email, or obtained according to variousways; and a slot 12560 via which the storage medium 12570 is loaded intothe mobile phone 12500. The storage medium 12570 may be a flash memory,e.g., a secure digital (SD) card or an electrically erasable andprogrammable read only memory (EEPROM) included in a plastic case.

FIG. 24 illustrates an internal structure of the mobile phone 12500,according to an embodiment. To systemically control parts of the mobilephone 12500 including the display screen 12520 and the operation panel12540, a power supply circuit 12700, an operation input controller12640, an image encoder 12720, a camera interface 12630, an LCDcontroller 12620, an image decoder 12690, a multiplexer/demultiplexer12680, a recorder/reader 12670, a modulator/demodulator 12660, and asound processor 12650 are connected to a central controller 12710 via asynchronization bus 12730.

If a user operates a power button and sets from a ‘power off’ state to a‘power on’ state, the power supply circuit 12700 supplies power to allthe parts of the mobile phone 12500 from a battery pack, thereby settingthe mobile phone 12500 in an operation mode.

The central controller 12710 includes a central processing unit (CPU), aROM, and a RAM.

While the mobile phone 12500 transmits communication data to theoutside, a digital signal is generated by the mobile phone 12500 undercontrol of the central controller 12710. For example, the soundprocessor 12650 may generate a digital sound signal, the image encoder12720 may generate a digital image signal, and text data of a messagemay be generated via the operation panel 12540 and the operation inputcontroller 12640. When a digital signal is transmitted to themodulator/demodulator 12660 under control of the central controller12710, the modulator/demodulator 12660 modulates a frequency band of thedigital signal, and a communication circuit 12610 performsdigital-to-analog conversion (DAC) and frequency conversion on thefrequency band-modulated digital sound signal. A transmission signaloutput from the communication circuit 12610 may be transmitted to avoice communication base station or the wireless base station 12000 viathe antenna 12510.

For example, when the mobile phone 12500 is in a conversation mode, asound signal obtained via the microphone 12550 is transformed into adigital sound signal by the sound processor 12650, under control of thecentral controller 12710. The digital sound signal may be transformedinto a transformation signal via the modulator/demodulator 12660 and thecommunication circuit 12610, and may be transmitted via the antenna12510.

When a text message, e.g., email, is transmitted in a data communicationmode, text data of the text message is input via the operation panel12540 and is transmitted to the central controller 12710 via theoperation input controller 12640. Under control of the centralcontroller 12710, the text data is transformed into a transmissionsignal via the modulator/demodulator 12660 and the communication circuit12610 and is transmitted to the wireless base station 12000 via theantenna 12510.

To transmit image data in the data communication mode, image datacaptured by the camera 12530 is provided to the image encoder 12720 viathe camera interface 12630. The captured image data may be directlydisplayed on the display screen 12520 via the camera interface 12630 andthe LCD controller 12620.

A structure of the image encoder 12720 may correspond to that of theabove-described video encoding method according to the embodiment. Theimage encoder 12720 may transform the image data received from thecamera 12530 into compressed and encoded image data based on theabove-described video encoding method according to the embodiment, andthen output the encoded image data to the multiplexer/demultiplexer12680. During a recording operation of the camera 12530, a sound signalobtained by the microphone 12550 of the mobile phone 12500 may betransformed into digital sound data via the sound processor 12650, andthe digital sound data may be transmitted to themultiplexer/demultiplexer 12680.

The multiplexer/demultiplexer 12680 multiplexes the encoded image datareceived from the image encoder 12720, together with the sound datareceived from the sound processor 12650. A result of multiplexing thedata may be transformed into a transmission signal via themodulator/demodulator 12660 and the communication circuit 12610, and maythen be transmitted via the antenna 12510.

While the mobile phone 12500 receives communication data from theoutside, frequency recovery and ADC are performed on a signal receivedvia the antenna 12510 to transform the signal into a digital signal. Themodulator/demodulator 12660 modulates a frequency band of the digitalsignal. The frequency-band modulated digital signal is transmitted tothe video decoding unit 12690, the sound processor 12650, or the LCDcontroller 12620, according to the type of the digital signal.

In the conversation mode, the mobile phone 12500 amplifies a signalreceived via the antenna 12510, and obtains a digital sound signal byperforming frequency conversion and ADC on the amplified signal. Areceived digital sound signal is transformed into an analog sound signalvia the modulator/demodulator 12660 and the sound processor 12650, andthe analog sound signal is output via the speaker 12580, under controlof the central controller 12710.

When in the data communication mode, data of a video file accessed at anInternet website is received, a signal received from the wireless basestation 12000 via the antenna 12510 is output as multiplexed data viathe modulator/demodulator 12660, and the multiplexed data is transmittedto the multiplexer/demultiplexer 12680.

To decode the multiplexed data received via the antenna 12510, themultiplexer/demultiplexer 12680 demultiplexes the multiplexed data intoan encoded video data stream and an encoded audio data stream. Via thesynchronization bus 12730, the encoded video data stream and the encodedaudio data stream are provided to the video decoding unit 12690 and thesound processor 12650, respectively.

A structure of the image decoder 12690 may correspond to that of theabove-described video decoding method according to the embodiment. Theimage decoder 12690 may decode the encoded video data to obtainreconstructed video data and provide the reconstructed video data to thedisplay screen 12520 via the LCD controller 12620, by using theabove-described video decoding method according to the embodiment.

Thus, the data of the video file accessed at the Internet website may bedisplayed on the display screen 12520. At the same time, the soundprocessor 12650 may transform audio data into an analog sound signal,and provide the analog sound signal to the speaker 12580. Thus, audiodata contained in the video file accessed at the Internet website mayalso be reproduced via the speaker 12580.

The mobile phone 12500 or another type of communication terminal may bea transceiving terminal including both a video encoding apparatus and avideo decoding apparatus according to an embodiment, may be atransceiving terminal including only the video encoding apparatus, ormay be a transceiving terminal including only the video decodingapparatus.

A communication system according to the embodiment is not limited to thecommunication system described above with reference to FIG. 24. Forexample, FIG. 25 illustrates a digital broadcasting system employing acommunication system, according to an embodiment. The digitalbroadcasting system of FIG. 25 may receive a digital broadcasttransmitted via a satellite or a terrestrial network by using a videoencoding apparatus and a video decoding apparatus according to anembodiment.

Specifically, a broadcasting station 12890 transmits a video data streamto a communication satellite or a broadcasting satellite 12900 by usingradio waves. The broadcasting satellite 12900 transmits a broadcastsignal, and the broadcast signal is transmitted to a satellite broadcastreceiver via a household antenna 12860. In every house, an encoded videostream may be decoded and reproduced by a TV receiver 12810, a set-topbox 12870, or another device.

When a video decoding apparatus according to an embodiment isimplemented in a reproducing apparatus 12830, the reproducing apparatus12830 may parse and decode an encoded video stream recorded on a storagemedium 12820, such as a disc or a memory card to reconstruct digitalsignals. Thus, the reconstructed video signal may be reproduced, forexample, on a monitor 12840.

In the set-top box 12870 connected to the antenna 12860 for asatellite/terrestrial broadcast or a cable antenna 12850 for receiving acable television (TV) broadcast, a video decoding apparatus according toan embodiment may be installed. Data output from the set-top box 12870may also be reproduced on a TV monitor 12880.

As another example, a video decoding apparatus according to anembodiment may be installed in the TV receiver 12810 instead of theset-top box 12870.

An automobile 12920 that has an appropriate antenna 12910 may receive asignal transmitted from the satellite 12900 or the wireless base station11700. A decoded video may be reproduced on a display screen of anautomobile navigation system 12930 installed in the automobile 12920.

A video signal may be encoded by a video encoding apparatus according toan embodiment and may then be stored in a storage medium. Specifically,an image signal may be stored in a DVD disc 12960 by a DVD recorder ormay be stored in a hard disc by a hard disc recorder 12950. As anotherexample, the video signal may be stored in an SD card 12970. If the harddisc recorder 12950 includes a video decoding apparatus according to anembodiment, a video signal recorded on the DVD disc 12960, the SD card12970, or another storage medium may be reproduced on the TV monitor12880.

The automobile navigation system 12930 may not include the camera 12530of FIG. 24, and the camera interface 12630 and the image encoder 12720of FIG. 24. For example, the computer 12100 and the TV receiver 12810may not include the camera 12530, the camera interface 12630, and theimage encoder 12720.

FIG. 26 is a diagram illustrating a network structure of a cloudcomputing system using a video encoding apparatus and a video decodingapparatus, according to an embodiment.

The cloud computing system may include a cloud computing server 14000, auser database (DB) 14100, a plurality of computing resources 14200, anda user terminal.

The cloud computing system provides an on-demand outsourcing service ofthe plurality of computing resources 14200 via a data communicationnetwork, e.g., the Internet, in response to a request from the userterminal. Under a cloud computing environment, a service providerprovides users with desired services by combining computing resources atdata centers located at physically different locations by usingvirtualization technology. A service user does not have to installcomputing resources, e.g., an application, a storage, an operatingsystem (OS), and security, into his/her own terminal in order to usethem, but may select and use desired services from among services in avirtual space generated through the virtualization technology, at adesired point in time.

A user terminal of a specified service user is connected to the cloudcomputing server 14000 via a data communication network including theInternet and a mobile telecommunication network. User terminals may beprovided cloud computing services, and particularly video reproductionservices, from the cloud computing server 14000. The user terminals maybe various types of electronic devices capable of being connected to theInternet, e.g., a desktop PC 14300, a smart TV 14400, a smart phone14500, a notebook computer 14600, a portable multimedia player (PMP)14700, a tablet PC 14800, and the like.

The cloud computing server 14000 may combine the plurality of computingresources 14200 distributed in a cloud network and provide userterminals with a result of combining. The plurality of computingresources 14200 may include various data services, and may include datauploaded from user terminals. As described above, the cloud computingserver 14000 may provide user terminals with desired services bycombining video database distributed in different regions according tothe virtualization technology.

User information about users who have subscribed for a cloud computingservice is stored in the user DB 14100. The user information may includelogging information, addresses, names, and personal credit informationof the users. The user information may further include indexes ofvideos. Here, the indexes may include a list of videos that have alreadybeen reproduced, a list of videos that are being reproduced, a pausingpoint of a video that was being reproduced, and the like.

Information about a video stored in the user DB 14100 may be sharedbetween user devices. For example, when a video service is provided tothe notebook computer 14600 in response to a request from the notebookcomputer 14600, a reproduction history of the video service is stored inthe user DB 14100. When a request to reproduce this video service isreceived from the smart phone 14500, the cloud computing server 14000searches for and reproduces this video service, based on the user DB14100. When the smart phone 14500 receives a video data stream from thecloud computing server 14000, a process of reproducing video by decodingthe video data stream is similar to an operation of the mobile phone12500 described above with reference to FIG. 24.

The cloud computing server 14000 may refer to a reproduction history ofa desired video service, stored in the user DB 14100. For example, thecloud computing server 14000 receives a request to reproduce a videostored in the user DB 14100, from a user terminal. If this video wasbeing reproduced, then a method of streaming this video, performed bythe cloud computing server 14000, may vary according to the request fromthe user terminal, i.e., according to whether the video will bereproduced, starting from a start thereof or a pausing point thereof.For example, if the user terminal requests to reproduce the video,starting from the start thereof, the cloud computing server 14000transmits streaming data of the video starting from a first framethereof to the user terminal. If the user terminal requests to reproducethe video, starting from the pausing point thereof, the cloud computingserver 14000 transmits streaming data of the video starting from a framecorresponding to the pausing point, to the user terminal.

In this case, the user terminal may include a video decoding apparatusas described above with reference to FIGS. 1 through 26. As anotherexample, the user terminal may include a video encoding apparatus asdescribed above with reference to FIGS. 1 through 26. Alternatively, theuser terminal may include both the video decoding apparatus and thevideo encoding apparatus as described above with reference to FIGS. 1through 26.

Various applications of a video encoding method, a video decodingmethod, a video encoding apparatus, and a video decoding apparatusaccording to the embodiment described above with reference to FIGS. 1through 26 have been described above with reference to FIGS. 13 through19. However, methods of storing the video encoding method and the videodecoding method in a storage medium or methods of implementing the videoencoding apparatus and the video decoding apparatus in a device,according to various embodiments, described above with reference toFIGS. 1 through 26 are not limited to the embodiments described abovewith reference to FIGS. 20 through 26.

As used herein, a technique “A may include one of a1, a2 and a3” is thatan element A may include an exemplary element a1, a2, or a3 in a widesense.

Due to the above-described technique, an element that may be includedthe element A is not necessarily limited to a1, a2 or a3. Thus, thetechnique is not exclusively construed that an element that may beincluded in A excludes other elements that are not exemplified, inaddition to a1, a2, and a3.

Further, the technique means that A may include a1, a2, or a3. Thetechnique does not mean that elements included in A are not necessarilyselectively determined within a predetermined set. For example, thetechnique is not limited to construe that a1, a2, or a3 selected from aset including a1, a2, and a3 is necessarily included in the component A.

In addition, in the present specification, a technique “at least one ofa1, a2, or (and) a3f” means one of a1; a2; a3; a1 and a2; a1 and a3; a2and a3; and a1 and a2, and a3.

Thus, unless explicitly described as “at least one of a1, at least oneof a2, or (and) at least one of a3”, the technique “at least one of a1,a2, or (and) a3” is not construed as “at least one of a1, at least oneof a2, or (and) at least one of a3”.

The embodiments may be written as computer programs and may beimplemented in general-use digital computers that execute the programsusing a computer-readable recording medium. Examples of thecomputer-readable recording medium include magnetic storage media (e.g.,ROM, floppy discs, hard discs, etc.) and optical recording media (e.g.,CD-ROMs, or DVDs).

It should be understood that embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments.

While embodiments have been described with reference to the figures, itwill be understood by those of ordinary skill in the art that variouschanges in form and details may be made therein without departing fromthe spirit and scope as defined by the following claims.

What is claimed is:
 1. A method of encoding an input image, comprising:by at least one processor, which executes instructions stored in atleast one memory, generating symbols by performing transformation andquantization based on a transformation block on which prediction isperformed according to a prediction mode, the transformation blockincluding at least a data unit of the input image; updating aprobability index of a current sub block by using a probability index ofa previous sub block among sub blocks included in the transformationblock; determining a rate according to a bit length of the current subblock by using the probably index; determining a rate of thetransformation block by using rates of the sub blocks; determining adistortion by using a difference between the input image and areconstruction image reconstructed according to the transformation andthe quantization; and determining a rate-distortion (R-D) cost by usingthe distortion and the rate.
 2. The image encoding method of claim 1,wherein at least one of the updating of the probability index of thecurrent sub block, the determining of the rate, the determining of therate of the transformation block, the determining of the distortion, andthe determining of the R-D cost are performed in parallel according toone sub block.
 3. The image encoding method of claim 1, wherein theprobability index of the current sub block is an index indicating aprobability that a bin value encoded by using a context used to encodethe current sub block is a least probable symbol (LPS).
 4. The imageencoding method of claim 3, wherein the updating of the probabilityindex of the current sub block comprises obtaining the probability indexof the current sub block by reflecting values and a number of generatedbins in a probability index of a context of the previous sub block. 5.The image encoding method of claim 1, wherein the determining of thedistortion comprises normalizing the distortion.
 6. The image encodingmethod of claim 5, wherein the normalizing the distortion is performedby using a quantization step size with respect to the R-D cost.
 7. Theimage encoding method of claim 1, further comprising: determining aprediction mode having a minimum R-D cost among R-D costs determined foreach of one or more prediction modes.
 8. An image encoding apparatusencoding an input image comprising: a symbol generator configured to:generate symbols by performing transformation and quantization based ona transformation block on which prediction is performed according to aprediction mode, the transformation block including at least a data unitof the input image; a rate determiner configured to: update aprobability index of a current sub block by using a probability index ofa previous sub block among sub blocks included in the transformationblock, determine a rate according to a bit length of the current subblock by using the probably index, and determine a rate of thetransformation block by using rates of the sub blocks; a distortiondeterminer configured to determine a distortion by using a differencebetween the input image and a reconstruction image reconstructedaccording to the transformation and the quantization; and arate-distortion (R-D) cost determiner configured to determine a R-D costby using the distortion and the rate.
 9. The image encoding apparatus ofclaim 8, wherein operations by at least one of the rate determiner, thedistortion determiner, and the R-D cost determiner are performed inparallel according to one sub block.
 10. The image encoding apparatus ofclaim 8, wherein the probability index of the current sub block is anindex indicating a probability that a bin value encoded by using acontext used to encode the current sub block is a least probable symbol(LPS).
 11. The image encoding apparatus of claim 10, wherein the ratedeterminer obtains the probability index of the current sub block byreflecting values and a number of generated bins in a probability indexof a context of the previous sub block.
 12. The image encoding apparatusof claim 8, wherein the distortion determiner performs normalizing thedistortion.
 13. The image encoding apparatus of claim 12, wherein thenormalizing is performed by using a quantization step size with respectto the R-D cost.
 14. The image encoding apparatus of claim 8, furthercomprising: a prediction mode determiner for determining a predictionmode having a minimum R-D cost among R-D costs determined for each ofone or more prediction modes.
 15. A non-transitory computer-readablerecording medium having recorded thereon a computer program forexecuting the method of claim 1.